Polycarbonate resins (PC) produced from bisphenol A and the like have been finding use in many materials for various parts in, for example, an electrical and electronic field, an automobile field, and an architecture field because the resins are excellent in thermal resistance, mechanical properties, dimensional stability, and the like. However, the polycarbonate resin has not obtained enough performance to be used as a material for an outdoor electrical and electronic storage box such as an information communication box, a junction box for photovoltaic power generation, or the like which requires an extremely high degree of impact characteristic at a low temperature of, for example, −40° C. and an extremely high degree of flame retardancy.
In the case of the conventional polycarbonate resin, high flame retardancy can be imparted by using a flame retardant or the like. However, a polycarbonate resin that brings together flame retardancy and a low-temperature impact characteristic, and shows satisfactory performance when put into practical use has not been obtained. For example, it has been known that the addition of an elastomer to the polycarbonate resin improves its impact characteristic. However, its impact characteristic at low temperature is not sufficient. In addition, increasing the molecular weight of the polycarbonate resin improves its low-temperature impact characteristic. However, the increase involves a problem in that its flowability reduces.
In view of the foregoing, a method involving using a copolymer of the polycarbonate resin and any other polymer has been investigated. One example of such copolymer is a polycarbonate-polydimethylsiloxane copolymer (PC-PDMS).
Although the polycarbonate-polydimethylsiloxane copolymer is superior in flame retardancy and low-temperature impact characteristic to the conventional polycarbonate resin, the polycarbonate-polydimethylsiloxane copolymer alone cannot obtain such a high degree of flame retardancy as V-0 based on the UL standard 94. In view of the foregoing, the following method has been proposed for obtaining high flame retardancy (Patent Literature 1). A polycarbonate-polydimethylsiloxane copolymer that has a branched chain and whose polydimethylsiloxane amount is set to 1 mass %, and an organometallic salt are used in combination. Although a maintaining effect on transparency and a preventing effect on a drip at the time of combustion can be expected from the method, the method involves the following drawback. Flowability and a low-temperature impact characteristic reduce.
Meanwhile, a method involving using the polycarbonate-polydimethylsiloxane copolymer, an organobromine compound, and an organometallic salt in combination has been proposed for achieving a high degree of flame retardancy while maintaining the low-temperature impact characteristic (Patent Literature 2). However, the method may result in the generation of dioxins as harmful substances at the time of the combustion of the resin because the organobromine compound is used. In addition, the method involves the following drawback because a polytetrafluoroethylene (PTFE) is added as a drip inhibitor. An impact characteristic at such a low temperature as −40° C. reduces.
In addition, a method involving using an impact modifier and a phosphate-based flame retardant in combination has been proposed with a view to achieving compatibility between the impact characteristic and the flame retardancy (Patent Literature 3). However, the method involves the following drawback because the phosphate-based flame retardant is used. Heat resistance reduces.
Meanwhile, a method involving adding a mixed powder formed of polytetrafluoroethylene particles and organic polymer particles, and a metal salt to a polycarbonate resin has been known (Patent Literatures 4 and 5). However, none of those literatures describes that extremely high flame retardancy and an extremely high low-temperature impact characteristic are obtained by selecting a polycarbonate-polydimethylsiloxane copolymer having a specific number of repetitions of a polydimethylsiloxane and a specific polydimethylsiloxane content as the polycarbonate resin.